yes..
set up 2 pools with different usernames, then on the first pools password put --load-balanced. i think or you can try --balanced.
or you can just send half the btc to his account?
also keep in mind power costs money, so anything you do wont be 50/50
I think you are on to something with just one BTC address. Load balance makes more sense if you were wanting to do some as PPS and some as Solo or something like that.
If you are mining and splitting costs just mine to one BTC and subtract costs, and divide it into your and his personal BTC address's weekly or so.